Four-layer seamed press fabric

ABSTRACT

An on-machine-seamable press fabric for the press section of a paper machine includes a multi-layered integrally woven base fabric having two systems of machine-direction yarns forming seaming loops along each of its two widthwise edges. A seaming spiral is attached to the seaming loops in both rows at each of the two widthwide edges. The two seaming spirals are used to join the press fabric into endless form during installation on the press section of a paper machine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the papermaking arts. Morespecifically, the present invention relates to a papermaker's fabric ofthe on-machine-seamable variety, such as an on-machine-seamable pressfabric for the press section of a paper machine.

2. Description of the Prior Art

During the papermaking process, a fibrous web is formed by depositing afibrous slurry, that is, an aqueous dispersion of cellulosic fibers, ona moving forming fabric in the forming section of a paper machine. Alarge amount of water is drained from the slurry through the formingfabric during this process, leaving the fibrous web on the surface ofthe forming fabric.

The newly formed web proceeds from the forming section to a presssection, which includes a series of press nips. The fibrous web passesthrough the press nips supported by a press fabric, or, as is often thecase, between two press fabrics. In the press nips, the fibrous web issubjected to compressive forces which squeeze water therefrom, and whichadhere the fibers in the web to one another to turn the fibrous web intoa sheet. The water is accepted by the press fabric or fabrics and,ideally, does not return to the web.

The web, now a sheet, finally proceeds to a dryer section, whichincludes at least one series of rotatable dryer drums or cylinders,which are internally heated by steam. The sheet itself is directed in aserpentine path sequentially around each in the series of drums by adryer fabric, which holds the web closely against the surfaces of thedrums. The heated drums reduce the water content of the sheet to adesirable level through evaporation.

It should be appreciated that the forming, press and dryer fabrics alltake the form of endless loops on the paper machine and function in themanner of conveyors. It should further be appreciated that papermanufacture is a continuous process which proceeds at considerablespeed. That is to say, the fibrous slurry is continuously deposited ontothe forming fabric in the forming section, while a newly manufacturedpaper sheet is continuously wound onto rolls after it exits from thedryer section.

Referring, for the moment, specifically to press fabrics, it should berecalled that, at one time, press fabrics were supplied only in endlessform. This is because a newly formed paper sheet is extremelysusceptible to marking in the press nip by any nonuniformity in thepress fabric or fabrics. An endless, seamless fabric, such as oneproduced by the process known as endless weaving, has a uniformstructure in both its longitudinal (machine) and transverse(cross-machine) directions. A seam, such as a seam which may be used toclose the press fabric into endless form during installation on a papermachine, represents a discontinuity in the uniform structure of thepress fabric. The use of a seam, then, greatly increases the likelihoodthat the paper sheet will be marked in a press nip.

Accordingly, the seam region of any workable on-machine-seamable pressfabric must generally behave under load, that is, under compression inthe press nip or nips, like the rest of the press fabric, and must havethe same permeability to water and to air as the rest of the pressfabric, in order to minimize, if not entirely avoid, the marking of thepaper product being manufactured by the seam region.

Despite the considerable technical obstacles presented by theserequirements, it remained highly desirable to develop anon-machine-seamable press fabric, because of the comparative ease andsafety with which it could be installed on the press section.Ultimately, these obstacles were overcome with the development of pressfabrics having seams formed by providing seaming loops on the crosswiseedges of the two ends of the fabric. The seaming loops themselves areformed by the machine-direction (MD) yarns of the fabric. A seam isformed by bringing the two ends of the press fabric together, byinterdigitating the seaming loops at one end of the fabric with those atthe other end, and by directing a so-called pin, or pintle, through thepassage defined by the interdigitated seaming loops to lock the two endsof the fabric together. Needless to say, it is much easier and far lesstime-consuming to install an on-machine-seamable press fabric, than itis to install an endless press fabric, on a paper machine.

There are several methods for producing a press fabric that can bejoined into endless form on the paper machine with such a seam. Onemethod is to flat-weave the press fabric, in which case the warp yarnswould be its machine-direction (MD) yarns. To form the seaming loops inthis method, the warp ends are woven some distance back into the fabricbody in a direction parallel to the warp yarns. Another technique, farmore preferable, is a modified form of endless weaving, which normallyis used to produce an endless loop of fabric. In modified endlessweaving, the weft, or filling, yarns are continuously woven back andforth across the loop, in each passage forming a loop on one of theedges of the fabric being woven by passing around a loop-forming pin. Asthe weft yarn, or filling yarn, which ultimately becomes the MD yarn inthe press fabric, is continuous, the seaming loops obtained in thismanner are stronger, and the seam formed with such seaming loops has agreater load-bearing capacity, than any that can be produced by weavingthe warp ends back into the ends of a flat-woven fabric. In stillanother method, a fabric is woven endless, and the endless loop offabric thereby obtained is flattened and given the form of two fabriclayers joined to one another at two widthwise ends of the flattenedloop. One or more widthwise yarns are then removed from each of the twowidthwise ends to produce a short gap defined by the freed, that is, thenewly unwoven portions of, lengthwise yarns at each end. These unwovenportions of the lengthwise yarns are then used as seaming loops when thetwo widthwise ends are brought together as described above.

For the manufacture of certain paper grades, such as linerboard andcorrugating media, press fabrics having high void volume and highwater-handling capacity are needed. Multi-layered press fabrics, such asthose shown in U.S. Pat. Nos. 4,865,083 and 4,887,648 to Cunnane, areuseful for such applications.

These patents issued from related applications, and show a method forseam formation for a press fabric having at least four machine-directionlayers. In the disclosed method, a woven base fabric, having at leastfour layers in the machine direction, is provided with seaming loops ateach of two ends to be joined together. The seaming loops finish atleast two of the layers. That is to say, at the two ends of the fabric,a machine-direction (MD) yarn from one of the at least four layers formsa seaming loop and reenters the fabric in another of the at least fourlayers, the same two layers being so related at each end, therebyfinishing the two layers in question. The remaining layers are finishedin a similar manner with or without seaming loops. By altering thechoice of which of the layers are finished in seaming loops, thegeometry of the seam can be varied.

The present invention is also a multi-layered press fabric, but isdesigned to be seamed into endless form during installation on a papermachine more readily than those shown in U.S. Pat. Nos. 4,865,083 and4,887,648.

SUMMARY OF THE INVENTION

Accordingly, the present invention is an on-machine-seamable pressfabric for the press section of a paper machine. The press fabriccomprises a system of first machine-direction (MD) yarns, a system ofsecond machine-direction (MD) yarns, and at least one system ofcross-machine-direction (CD) yarns. The CD yarns are interwoven with thesystems of first and second MD yarns to form an integrally wovenmulti-layered structure in a rectangular shape with a length, a width,two lengthwise edges and two widthwise edges. The first and second MDyarns form first and second seaming loops, respectively, along each ofthe two widthwise edges. The first and second seaming loops may be intwo distinct rows separated from one another in a thicknesswisedirection of the press fabric.

A first seaming spiral is attached to at least one of the first andsecond seaming loops at one of the two widthwise edges of the pressfabric by a first pintle. Similarly, a second seaming spiral is attachedto at least one of the first and second seaming loops at the other ofthe two widthwise edges of the press fabric by a second pintle.

The on-machine-seamable press fabric is joined into endless form duringinstallation on the press section of a paper machine by interdigitatingthe coils of the first and second seaming spirals and by directing athird pintle through the passage defined by the interdigitated coils.

The present invention will now be described in more complete detail,with frequent reference being made to the drawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the on-machine-seamable pressfabric of the present invention;

FIG. 2 is a cross-sectional view taken as indicated by line 2—2 in FIG.1;

FIG. 3 is a cross-sectional view taken as indicated by line 3—3 in FIG.1;

FIGS. 4a through 4 c are schematic views, analogous to that shown inFIG. 3, of alternate embodiments of the invention shown in that figure;and

FIGS. 5a through 5 c are further schematic views of alternateembodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now specifically to the figures, FIG. 1 is a schematicperspective view of an on-machine-seamable press fabric 10. The pressfabric 10 takes the form of an endless loop once its two ends 12, 14have been joined to one another at seam 16.

FIG. 2 is a cross-sectional view of press fabric 10 taken as indicatedby line 2—2 in FIG. 1. As such, the cross section is taken in thetransverse, or cross-machine, direction, and shows itscross-machine-direction (CD) yarns from the side and itsmachine-direction (MD) yarns in cross section.

As shown, on-machine-seamable press fabric 10 is an integrally wovenfour-layered structure comprising four layers 20,22,24,26 of MD yarns.The press fabric 10 is woven in accordance with a modified endlessweaving process as described above, and has a system of first MD yarns32 and a system of second MD yarns 34. First MD yarns 32 form the toptwo layers 20,22 in FIG. 2, and second MD yarns 34 form the bottom twolayers 24,26. First MD yarns 32 and second MD yarns 34 are weft yarnsduring the weaving process, and, as will be seen below, form seamingloops at two widthwise edges of the on-machine-seamable press fabric 10.

The system of first MD yarns 32 and the system of second MD yarns 34 areinterwoven with at least one system of CD yarns 36, which are the warpyarns during the weaving process. It should be understood that the weavepattern shown is only an example of the many which may be used for thispurpose.

First MD yarns 32, second MD yarns 34 and CD yarns 36 may each be of anyof the yarn types used to weave paper machine clothing. That is to say,monofilament yarns, which are monofilament strands used singly, orplied/twisted yarns, in the form of plied monofilament or pliedmultifilament yarns may be used as any of these yarns.

Further, the filaments comprising first MD yarns 32, second MD yarns 34and CD yarns 36 are extruded from synthetic polymeric resin materials,such as polyamide, polyester, polyetherketone, polypropylene,polyaramid, polyolefin and polyethylene terephthalate (PET) resins, andincorporated into yarns according to techniques well-known in thetextile industry and particularly in the paper machine clothingindustry.

FIG. 3 is a cross-sectional view of seam 16 of on-machine-seamable pressfabric 10 taken as indicated by line 3—3 in FIG. 1. First MD yarns 32form first seaming loops 42 at the two ends 12,14 of the press fabric10. Likewise, second MD yarns 34 form second seaming loops 44 at the twoends 12,14. First seaming loops 42 and second seaming loops 44 form tworows extending along the widthwise edges of press fabric 10. As shown,the first seaming loops 42 are vertically stacked relative to the secondseaming loops 44, although it should be understood that they may also belongitudinally offset from one another in the machine direction.

As stated previously, press fabric 10 is integrally woven according to amodified endless weaving process. First seaming loops 42 and secondseaming loops 44 are formed by first MD yarns 32 and second MD yarns 34,respectively, both of which are weft yarns during the weaving process.First seaming loops 42 and second seaming loops 44 are each formed by aseparate loop-forming pin. At the conclusion of the weaving process, theloop-forming pins (not illustrated) are removed to produce an open-endedfabric having the above-described two rows of seaming loops, one rowbeing of first seaming loops 42 and the other row being of secondseaming loops 44, along the widthwise edges of the press fabric 10.

In accordance with the present invention, a seaming spiral 52 isconnected to each of the two ends 12,14 of the press fabric 10. Theseaming spirals 52 are connected to both of the first seaming loops 42and second seaming loops 44 at each of the two ends of the press fabric10 by pintles 62 and pintles 64, respectively. The seaming spirals 52may be attached to the two ends 12,14 concurrently with the removal ofthe loop-forming pins. This may be necessary where either the first MDyarns 32 or the second MD yarns 34 are plied/twisted yarns, sinceseaming loops formed therefrom tend to rotate from the ideal geometryrequired for interdigitation and seaming, and tend to be easilydeformed. Alternatively, the seaming spirals 52 may be attached to theseaming loops 42,44 at the two ends 12,14 of the press fabric 10 at alater time during its processing, such as, for example, after staplefiber material has been needled thereinto, the loop-forming pin removedand the seaming loops 42,44 at the two ends 12,14 separated from oneanother.

Pintles 62 and pintles 64 may be single strands of monofilament;multiple strands of monofilament untwisted about one another, or plied,twisted, braided or knitted together; or of any of the other pintletypes used to close seams in paper machine clothing. These pintles 62,64may be extruded from the same synthetic polymeric resin materials as areused to produce the yarns 32,34,36 from which the press fabric 10 iswoven.

As for the seaming spirals 52, they are monofilament spirals extrudedfrom a polymeric resin material, which is preferably a polyamide resin,but could also be a polyester, polyetherketone, polypropylene,polyolefin or polyethylene terephthalate (PET) resin. The monofilamentdiameter may be, for example, 0.40 mm or 0.50 mm. During theinstallation of press fabric 10 on a paper machine, seaming spirals 52,being of monofilament, may be readily interdigitated with one anotherand joined to one another by directing pintle 66 through the passagedefined by the interdigitated coils of the seaming spirals 52. Stufferyarns may be inserted within the seaming spirals 52 to ensure that seam16 has permeability characteristics similar to those of the rest of thefabric 10.

Like pintles 62 and pintles 64, pintle 66 may be a single strand ofmonofilament; multiple strands of monofilament untwisted about another,or plied, twisted, braided or knitted together; or of any of the otherpintle types used to close seams in paper machine clothing. Pintle 66may alternatively be shaped, which is to say that it may have anon-circular cross section, so that it will properly fill the volumewithin the interdigitated seaming spirals 52 to ensure that the caliperand pressure uniformity of seam 16 is like that of the body of thefabric 10. Moreover, pintles 66 may also be extruded from the samesynthetic polymeric resin materials as are used to produce the yarns32,34,36 from which the press fabric 10 is woven.

Several layers of staple fiber material 68 may be attached to each sideof press fabric 10 and entangled through its structure by needling orhydroentanglement. For the sake of clarity, staple fiber material 68 isshown in only a portion of FIG. 3. Staple fiber material 68 may comprisestaple fibers of a polymeric resin material, such as polyamide orpolyester.

The importance that the seam area of the fabric has characteristics offlow resistance and uniformity of pressure distribution like those ofthe body of the fabric is well known. This is necessary to prevent thewet paper sheet from being marked by the seam as it passes through apress nip with the fabric. A four-layer integrally woven fabric havingone set of seaming loops at each end marks a wet paper sheet due to thesignificant difference between the aforementioned characteristics of theseam and the body of the fabric. A four-layer integrally woven fabrichaving two sets of seaming loops at each end does not mark a wet papersheet as seriously, but is more difficult to join into endless form on apaper machine than one having a single set of seaming loops at each end.The seaming spirals of the present invention make it easier and fasterto do so because only one pintle is required to close the seam. Thespiral spacing and uniformity are also better than those of woven loops,contributing to the ease and speed with which the fabric may be joinedinto endless form. Further, it is well known that anynon-single-monofilament yarn, either twisted (cabled, plied, etc.) oruntwisted, forms a seaming loop having a poor geometry relative toadjacent seaming loops, or a more pliable loop relative thereto. Ineither case, it becomes difficult to interdigitate the seaming loops ona paper machine to form a seam. If one or both of the sets of seamingloops are formed by yarns of the non-single-monofilament type, it isdifficult, if not impossible, to join the fabric into the form of anendless loop in a timely manner. The seaming spirals of the presentinvention permit yarns other than single monofilaments to be used tocustom-design fabric properties, such as dewatering, compressibility andvoid volume, in a fabric that is relatively easy to install on a papermachine.

To further reduce the difference between the properties of the seam andof the fabric body, not only can the type and geometry of all threepintles 62,64,66 be selected, but stuffer yarns can also be insertedwithin the intermeshed seaming spirals. Seam modifications can alsoinclude the weaving in of additional yarns at seaming loops 42,44 inaccordance with the teachings of U.S. Pat. Nos. 5,476,123 and 5,531,251,which teachings are incorporated herein by reference. Moreover, theseaming loops 42,44, the seaming spirals 52, and the volume defined bythe interdigitated seaming spirals 52 and occupied by the pintle 66 caninclude flow-resistant materials. For example, the flow-resistantmaterials may be additional CD yarns, such as monofilament,multifilament, texturized, braided, knitted or spun yarns of appropriateweight and size to provide a required level of flow resistance. Theadditional CD yarns may have cross sections of circular, oval,rectangular, lobed or other shapes, and may be of the same type as ordifferent from the functional CD yarns 36. Alternatively, theflow-resistant materials may be a ribbon of woven or non-woven materialor of polymeric film, or a polymeric foam or liquid resin cured toprovide a desired additional flow resistance.

Modifications to the above would be obvious to those of ordinary skillin the art, but would not bring the invention so modified beyond thescope of the appended claims. For example, first seaming loops 42 andsecond seaming loops 44 may extend an equal amount in a lengthwisedirection from the widthwise edges of the press fabric 10, as shown inFIG. 3. Alternatively, first seaming loops 42 and second seaming loops44 may extend a different amount in a lengthwise direction from saidwidthwise edges, as shown in FIGS. 4a through 4 c. In FIG. 4a, seamingloops 42 are longer than seaming loops 44 at both ends of the pressfabric 10. In FIG. 4b, the reverse is the case—seaming loops 44 arelonger than seaming loops 42 at both ends of the press fabric 10. InFIG. 4c, seaming loop 42 is longer than seaming loop 44 at one end ofthe press fabric 10, while the reverse is the case at the other end.

Alternatively, first MD yarns 32 may form the top and bottom layers20,26 in FIG. 2, and second MD yarns 34 may form the middle two layers22,24. In such a situation, illustrated in FIGS. 5a through 5 c, firstMD yarns 32 form first seaming loops 72, and second MD yarns 34 formsecond seaming loops 74, along the widthwise edges of the press fabric10. In FIG. 5a, seaming loops 72 are longer than seaming loops 74 atboth ends of the press fabric 10. In FIG. 5b, seaming loops 72 andseaming loops 74 extend the same amount from both ends of the pressfabric 10. Finally, in FIG. 5c, seaming loops 74 are longer than seamingloops 72 at both ends of the press fabric 10. Because of the unequallengths of seaming loops 72 and seaming loops 74 in FIGS. 5a and 5 c,seaming spirals 52 may be joined to only one of the two seaming loops72,74 at each end of the press fabric 10.

Other modifications may become apparent to those of ordinary skill inthe art.

What is claimed is:
 1. An on-machine-seamable press fabric for the presssection of a paper machine, said press fabric comprising: a system offirst machine-direction (MD) yarns, a system of second machine-direction(MD) yarns, and at least one system of cross-machine-direction (CD)yarns, said at least one system of CD yarns being interwoven with saidsystems of first and second MD yarns to form an integrally wovenmulti-layered structure in a rectangular shape with a length, a width,two lengthwise edges and two widthwise edges, said first and second MDyarns forming first and second seaming loops, respectively, along eachof said two widthwise edges thereof; a first seaming spiral attached toat least one of said first and second seaming loops at one of said twowidthwise edges of said press fabric by a first pintle; a second seamingspiral attached to at least one of said first and second seaming loopsat the other of said two widthwise edges of said press fabric by asecond pintle, whereby said press fabric is joined into endless formduring installation on the press section of a paper machine byinterdigitating the coils of said first and second seaming spirals andby directing a third pintle through the passage defined by theinterdigitated coils of said first and second seaming spirals.
 2. Anon-machine seamable press fabric as claimed in claim 1 wherein saidfirst and second seaming loops are in two distinct rows separated fromone another in a thicknesswise direction of the press fabric.
 3. Anon-machine-seamable press fabric as claimed in claim 2 wherein said twodistinct rows of said first and second seaming loops are verticallystacked relative to one another.
 4. An on-machine-seamable press fabricas claimed in claim 3 wherein said first and second seaming loops extendan equal amount in a lengthwise direction from said widthwise edges. 5.An on-machine-seamable press fabric as claimed in claim 3 wherein saidfirst and second seaming loops extend a different amount in a lengthwisedirection from said widthwise edges.
 6. An on-machine-seamable pressfabric as claimed in claim 2 wherein said two distinct rows of saidfirst and second seaming loops are offset from one another in alengthwise direction.
 7. An on-machine-seamable press fabric as claimedin claim 2 wherein said first seaming spiral is attached to both of saidfirst and second seaming loops at one of said two widthwise edges ofsaid press fabric by said first pintle and a fourth pintle,respectively; and wherein said second seaming spiral is attached to bothof said first and second seaming loops at the other of said twowidthwise edges of said press fabric by said second pintle and a fifthpintle, respectively.
 8. An on-machine-seamable press fabric as claimedin claim 1 wherein said first and second seaming loops extend adifferent amount in a lengthwise direction from said widthwise edges. 9.An on-machine-seamable press fabric as claimed in claim 1 wherein saidfirst and second seaming loops extend an equal amount in a lengthwisedirection from said widthwise edges.
 10. An on-machine-seamable pressfabric as claimed in claim 1 wherein said first seaming spiral isattached to both of said first and second seaming loops at one of saidtwo widthwise edges of said press fabric by said first pintle; andwherein said second seaming spiral is attached to both of said first andsecond seaming loops at the other of said two widthwise edges of saidpress fabric by said second pintle.
 11. An on-machine-seamable pressfabric as claimed in claim 1 wherein said first and second seamingspirals are monofilament spirals.
 12. An on-machine-seamable pressfabric as claimed in claim 11 wherein said monofilament spirals areextruded from a polymeric resin material.
 13. An on-machine-seamablepress fabric as claimed in claim 12 wherein said polymeric resinmaterial is selected from the group consisting of polyamide, polyester,polyetherketone, polypropylene, polyolefin and polyethyleneterephthalate (PET) resins.
 14. An on-machine-seamable press fabric asclaimed in claim 1 wherein said system of first MD yarns forms twolayers of said integrally woven multi-layered structure.
 15. Aon-machine-seamable press fabric as claimed in claim 1 wherein saidsystem of second MD yarns forms two layers of said integrally wovenmulti-layered structure.
 16. An on-machine-seamable press fabric asclaimed in claim 1 wherein said first MD yarns and said second MD yarnsare weft yarns, and said CD yarns are warp yarns, during a modifiedendless weaving process by which said fabric is produced.
 17. Anon-machine-seamable press fabric as claimed in claim 1 wherein aplurality of layers of staple fiber material are attached to at leastone side thereof.
 18. An on-machine-seamable press fabric as claimed inclaim 17 wherein said staple fiber material comprises staple fibers of apolymeric resin material.